Biocomposites of hydroxyapatite, HAp, in conjunction with various binders including poly(vinyl alcohol), PVA, and collagen have the potential of serving in various tissue engineering applications, such as in bone repair and reconstruction tasks, especially if the nanoparticles of hydroxyapatite are used. Here, hydroxyapatite nanoparticles (n-HAp) were synthesized at the ultimate size range of 10-50 nm and then incorporated into PVA or in situ synthesized in collagen/PVA. The biocomposites of HAp with PVA exhibited relatively high elasticity (as revealed by the linear viscoelastic material functions, characterized upon small-amplitude oscillatory shear) especially upon cryogenic treatment. The incorporation of the collagen into the PVA/HAp biocomposite provided internal porosity to the biocomposite with the pores in the 50-100 nm range for collagen/HAp and 50-500 nm for the collagen/HAp/PVA. (c) 2006 Elsevier B.V. All rights reserved.